• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.44-48
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• 2007

In recent years, the size of plane substrates and semiconductor wafers has increased. As conventional contact transportation systems composed of, for example, carrier rollers, belt conveyers, and robot hands carry these longer and wider substrates, the increased weight results in increased potential for fracture. A noncontact transportation system is required to solve this problem. We propose a new noncontact transportation system combining acoustic viscous and aerostatic forces to provide damage-free transport. In this system, substrates are supported by aerostatic force and transported by acoustic viscous streaming induced by traveling wave deformation of a disk-type stator. A ring-type piezoelectric transducer bonded on the stator excites vibration. A stator with a high Q piezoelectric transducer can generate traveling vibrations with amplitude of $3.2{\mu}m$. Prior to constructing a carrying road for substrates, we clarified the basic properties of this technique and stator vibration characteristics experimentally. We constructed the experimental equipment using a rotational disk with a 95-mm diameter. Electric power was 70 W at an input voltage of 200 Vpp. A rotational torque of $8.5\times10^{-5}Nm$ was obtained when clearance between the stator and disk was $120{\mu}m$. Finally, we constructed a noncontact transport apparatus for polycrystalline silicon wafers $(150(W)\times150(L)\times0.3(t))$, producing a carrying speed of 59.2 mm/s at a clearance of 0.3 mm between the stator and wafer. The carrying force when four stators acted on the wafer was $2\times10^{-3}N$. Thus, the new noncontact transportation system was demonstrated to be effective.

• 대한기계학회논문집
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• 제15권1호
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• pp.229-240
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• 1991

본 연구에서 사용한 이론과 제시된 방법의 타당성을 검토하기 위하여 익열 간 극이 무한대인 단일 익형 주위의 유동장을, 최근에 개발된 계산방법인 Lambda방법을 사용한 Dadone의 해석결과와 비교하였고, 범용의 압축기 익형인 NACA65게열 익열 유동 에 대한 Herrig의 실험값, 그리고 미분해석에 의한 점성-비점성 상호작용 방법을 사용 한 Hansen의 계산값고, 이들 조건과 동일한 상태에서 본 연구에서 제시한 방법으로 계 산한 결과와 만족할 만한 일치를 얻었다.

• Advances in Computational Design
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• 제2권1호
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• pp.71-87
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• 2017

This study focuses on the efficiency and applicability of dynamic relaxation methods in form-finding of membrane structures. Membrane structures have large deformations that require complex nonlinear analysis. The first step of analysis of these structures is the form-finding process including a geometrically nonlinear analysis. Several numerical methods for form-finding have been introduced such as the dynamic relaxation, force density method, particle spring systems and the updated reference strategy. In the present study, dynamic relaxation method (DRM) is investigated. The dynamic relaxation method is an iterative process that is used for the static equilibrium analysis of geometrically nonlinear problems. Five different examples are used in this paper. To achieve the grading of the different dynamic relaxation methods in form-finding of membrane structures, a performance index is introduced. The results indicate that viscous damping methods show better performance than kinetic damping in finding the shapes of membrane structures.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.59-63
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• 2001

A high-impulse, low-power, continuous-shot microthruster has been developed using low boiling temperature liquid-propellant with high viscous fluid-plug. The viscous friction force of the fluid-plug increases the blast pressure and the low boiling temperature liquid-propellant is intended to reduce input power consumption. The three-layer microthruster has been fabricated by surface micromachining as well as bulk micromachining in the size of $7{\times}13{\times}1.5mm^{3}$. A continuous output impulse bit of $6.4{\times}10^{-8}N{\cdot}sec$ has been obtained from the fabricated microthruster using perfluoro normal hexane (FC72) propellant and oil plug, resulting in about ten times increase of the impulse bit using one hundredth electrical input energy compared to the conventional continuous microthruster.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.717-720
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• 2002

An Amplitude Proportional Friction Damper (APFD) system is considered in order to improve the stick-slip characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. The free vibration analysis on an 1-DOF system has conducted to demonstrate the characteristics of the APFD system and the results show that the APFD system has similar damping characteristics to the viscous damper system. It is concluded that the APFD system may become a cost effective substitution for the viscous damper and it also has certain advantages over Coulomb damper system since the APFD system can be designed to work with no stick-slip.

• 한국안광학회지
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• 제13권1호
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• pp.5-13
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• 2008

목적: 각막 부착 콘택트렌즈에는 어떠한 힘이 작용하며 또한 이 힘에 따른 렌즈의 운동을 알아보고자 본 해설을 작성하였다. 방법: 렌즈 아래 눈물층에는 모세관작용에 따른 힘이 발생하고 렌즈 회전에 따른 눈물층 간격변화에 기인하는 복원력이 발생한다. 눈깜빡임에 따라 콘택트렌즈는 눈꺼풀-렌즈 사이 마찰력과 눈꺼풀의 가속도에 의한 힘, 눈물층의 복원력 및 점성저항력에 의해 운동(움직임)이 결정된다. 눈깜빡임 도중/후 매순간 렌즈의 위치를 예측할 수 있는 미분방정식과 그 수치계산 프로그램 모델을 수립하였다. 이 컴퓨터 모델을 사용하여 눈깜빡임 주기, 렌즈의 BC, 눈꺼풀 압력 변화에 따른 매 순간 렌즈 위치를 예측할 수 있었다. 결과: 눈깜빡임 주기가 길수록, 눈꺼풀 압력이 클수록 눈꺼풀에 의한 마찰력 영향이 커져 렌즈 움직임이 커지며 BC가 증가할수록 눈물층 간격이 증가하여 점성저항력이 감소하며 따라서 렌즈 움직임이 커지는 것을 알 수 있었다. 눈깜빡임 후 렌즈는 눈물층 간격 변화에 따른 복원력과 눈물층의 점성저항력에 의해 진폭이 감소하는 진동을 하면서 평형위치로 복귀하게 된다. 이 경우 BC가 증가할수록 저항력이 감소하여 평형 위치로의 접근이 빨라진다. 결론: 콘택트렌즈의 움직임은 렌즈-각막 사이 눈물층의 물성 및 형상과 아울러 눈깜빡임에 의해 지배된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.456-462
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• 2001

Comprehensive numerical computations are made of a homogenous spin-up in a cylindrical cavity with a time-dependent rotation rate. Numerical solutions are acquired to the governing axisymmetric cylindrical Navier-Stokes equation. A rotation rate formula is ${\Omega}_f={\Omega}_i+{\Delta}{\Omega}(1-{\exp}(-t/t_c))$. If $t_c$ is large, it implies that a rotation change rate is small. The Ekman number, E, is set to $10^{-4}$ and the aspect ratio, R/H, fixed to I. For a linear spin-up(${\epsilon}<<$), the major contributor to spin-up in the interior is not viscous-diffusion term but inviscid term, especially Coriolis term, though $t_c$ is very large. The viscous-diffusion term only works near sidewall. But for spin-up from rest, when $t_c$ is very large, viscous-diffusion term affects interior area as well as sidewall, initially. So azimuthal velocity of interior for large $t_c$ appears faster than that of interior for relatively small $t_c$. However, the viscous-diffusion term of interior decreases as time increases. Instead, inviscid term appears in the interior.

• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.202-208
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• 2017

최근 개발된 선박용 주기관은 추진효율 향상과 연료소비율 저감기술이 요구됨에 따라 과거에 비해 높은 비틀림진동 기진력 특성을 갖고 있다. 따라서 이를 제어하기 위해 기본적으로 엔진 선단에 점성 댐퍼나 점성-스프링댐퍼를 장착한다. 점성댐퍼의 경우 댐퍼 내부에 채워진 실리콘 오일이 탄성적인 연결이 없다고 가정하고 댐퍼설계를 하여 왔으나 고점도 실리콘 오일은 높은 점도에 따른 비틀림 강성이 존재할 뿐만 아니라 작동온도와 주파수에 따라 비선형적인 동특성을 갖는다. 본 논문에서는 고점도 실리콘 오일이 적용된 점성댐퍼의 동특성을 확인하고 해당 댐퍼가 장착된 축계의 비틀림진동 특성을 검토하였다. 이를 위해 점성댐퍼의 최적 동특성을 이론적으로 해석하는 방법을 검토하였고, 고점도 실리콘 오일로 채워진 점성댐퍼로 해당축계의 비틀림진동 제어를 하는 경우 댐퍼 작동온도 및 경년변화를 고려한 추진축계 최적 설계 방안에 대해서 검토하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.998-999
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• 2014

This paper proposes a method for damping force modeling of magnetorheological (MR) damper featuring bypass hole. After describing configuration and of the MR damper, a damping force modeling of the MR damper is derived based on Bingham model of MR fluid. MR damper consists of piston, accumulator, gap, bypass hole and coil. Damping force is consists of spring force induced by accumulator, viscous force induced at gap and bypass hole, and controllable force induced at gap.

• Tribology and Lubricants
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• 제20권3호
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• pp.163-167
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• 2004

Reducing friction torque of the oil hydraulic vane pump used as the power source of power steering system should consider friction torque including viscous and mechanical friction torque according to the changes of rpm and pressure. This paper analyzes the forces acting on the vane to reduce the friction torque of the vane of the hydraulic vane pump used for Hydraulic Power Steering(HPS) system, and futhermore, the forces according to the shapes of cam profiles are analyzed.